Information recording medium, method and apparatus for manufacturing the same

ABSTRACT

An information recording medium of the present invention includes recording layers  19  and  26  whose phase can change by an optical or an electrical system so as to be detectable, and interface layers  18, 20, 25  and  27 , which are in contact with the recording layers  19  and  26 , to serve as oxide layers. The recording layer  19  contains a Ge—Bi—Te-M material represented by a formula: Ge α Bi β Te γ M 100-α-β-γ  (atom %), where M denotes at least one element selected from Al, Ga, In and Mn, and α, β and γ satisfy 25≦α≦60, 0&lt;β≦18, 35≦γ≦55, and 82≦α+β+γ&lt;100. The interface layers  18, 20, 25  and  27  contain at least one oxide of the element M contained in the recording layers  19  and  26.

TECHNICAL FIELD

The present invention relates to an information recording medium on andfrom which information is recorded and reproduced at high speed and highdensity. The present invention also relates to a method and an apparatusfor manufacturing the same.

BACKGROUND ART

The present inventors have developed a 4.7 GB DVD-RAM and a 25 GB,one-sided single-layer (1× speed) Blu-ray Disc as high-capacity,phase-change optical discs that can be used for data files and imagefiles. And from the viewpoint of increasing the recording capacity ofthe optical discs, the present inventors further have developed a 50 GB(1× speed) Blu-ray Disc having two information layers on one side forthe first time. These discs already have been commercialized.

A phase-change recording method, by which these DVD-RAM and Blu-raydiscs are recorded, utilizes the fact that a recording layer reversiblychanges its state between amorphous and crystalline (or betweencrystalline and another crystalline with a different structure) by beingirradiated with a laser beam. Recording is performed by irradiating aninformation recording medium with a laser beam to change at least eitherone of the refractive index and the extinction coefficient of a thinfilm. In the recorded portion, the amplitude of transmitted light orreflected light changes, and as a result, the amount of the transmittedlight or the reflected light changes when reaching a detecting system.The detecting system detects this change to reproduce signals.Generally, it is regarded as an unrecorded state when a recording layermaterial is in a crystalline state. Signals are recorded by irradiatingan information recording medium with a laser beam, melting the recordinglayer material, and then rapidly cooling the recording layer materialsto change it into an amorphous state. In order to erase the signals, theinformation recording medium is irradiated with a laser beam power lowerthan that used for recording to change the recording layer into acrystalline state. Phase-change optical discs generally have adielectric layer, a recording layer and a reflective layer formed on asubstrate. Examples of the configuration of such a disc include aconfiguration in which a first dielectric layer, a recording layer, asecond dielectric layer and a reflective layer are stacked sequentiallyon a substrate.

The following explains the role of each layer. The role of thedielectric layer includes protecting the recording layer from mechanicaldamage from the outside, emphasizing optical changes using interferenceeffects due to multiple reflections, blocking the influence of outsideair to prevent chemical changes, and reducing roughening of thesubstrate surface and thermal damage of the recording layer in the casewhere signals are recorded repeatedly. The dielectric layer sometimes isreferred to as a protective layer. Moreover, the speed of thecrystalline-amorphous state change of the recording layer depends mainlyon the composition of the dielectric layer (also referred to as aninterface layer), which is in contact with the recording layer. Thus,the dielectric layer has another important role in controlling acrystallization rate. The recording layer absorbs the laser beam aspreviously described and undergoes the crystalline-amorphous statechange, and thereby information is recorded on the recording layer. Therole of the reflective layer is to diffuse the heat generated from therecording layer that becomes hot through the laser beam absorption whilerecording and erasing information.

The present inventors have developed a single-sided dual-layer Blu-raydisc. Single-sided multilayer discs typified by a single-sideddual-layer disc have a plurality of information layers (a firstinformation layer 2, a second information layer 4, a third informationlayer 6, . . . , an n-th information layer 8 (where n is an integer of 4or more)) on a substrate 1 as shown in FIG. 2. Each of transparentoptical separation layers 3, 5, and 7, which are formed using anultraviolet curable resin or the like, is interposed between theinformation layers (between an information layer and another informationlayer) that are adjacent to each other. Further on top of it (on then-th information layer 8 in the structure shown in FIG. 2), a coverlayer 9 (an optically transparent layer) formed using, for example, theultraviolet curable resin is provided. In order to record or reproduceinformation on or from each of the information layers, a laser beam 10is incident on each of the information layers from the side of the coverlayer 9.

Current requirements for information recording media are to have anincreased capacity and being available for increased speeds (recordingand reproducing information at higher speeds). Developments areproceeding also for Blu-ray disc with an aim of recording andreproducing at a speed within a range of 1× to 2× (9.8 m/s linearvelocity) or a range of 1× to 4× (19.7 m/s linear velocity) with respectto the 1× (4.9 m/s linear velocity) recording that already has beencommercialized. The present inventors are currently developing a disc tobe available for a speed of 1× to 2×.

In phase-change recording, the crystallization rate is adjusted bychanging the composition of the recording layer according to a specifiedlinear velocity. When the linear velocity is high, the crystallizationrate is increased to make erasure easy. This, however, tends to spoilthe stability of recording marks (amorphous phase). When the linearvelocity is low, recording becomes easy by decreasing thecrystallization rate, but the amorphous phase becomes too stable andthereby a reliability problem arises in that erasure becomes difficult.In order to solve such a problem associated with high speed discs, thepresent inventors have found Ge—Bi—Te—M (M denotes at least one elementselected from Al, Ga, In, and Mn) as a composition for the recordinglayer.

The higher the linear velocity becomes, the more laser power (recordingsensitivity) is required for recording information. Under such acondition, in order to solve the above-mentioned problem and to improverepetitive rewriting performance, an oxide-based material layercontaining Hf or a mixture of Zr and Hf, at least one element selectedfrom a group consisting of La, Ce, Al, Ga, In, Mg and Y, and oxygen isdisclosed as a dielectric layer (including an interface layer) that hasbeen reported so far (refer to JP2005-56545A, for example).

In this way, the compositions of the materials for the recording layerand the dielectric layer (including the interface layer) are beingstudied in order to ensure recording and reproducing properties andreliability (repetitive recording) as the speeds become higher.

The following problem arose in increasing the speed of the Blu-ray disc(1× to 2×) that has been under development by the present inventors.

A high temperature humidity test (moisture resistance test), which isone of the lifetime tests, was conducted on a disc. For the recordinglayer thereof, a Ge—Bi—Te—M material, where M denotes at least oneelement selected from Al, Ga, In, and Mn, was used. For the layer (thedielectric layer (the interface layer)) that is in contact with therecording layer, a material containing a Zr oxide as its main componentwas used. A problem however, arose that the recording layer wasseparated from that layer (the dielectric layer (interface layer)). Inorder to deal with this problem, various film forming conditions(sputtering power, sputtering gas pressure and additive gas) wereexamined for the recording layer and the dielectric layer (interfacelayer), but the separation could not be suppressed.

DISCLOSURE OF INVENTION

The present invention is intended to provide a highly reliableinformation recording medium in which separation between a recordinglayer and another layer that is in contact with the recording layer issuppressed. The present invention also is intended to provide a methodand an apparatus for manufacturing the information recording medium.

The information recording medium of the present invention includes arecording layer whose phase can change by an optical or an electricalsystem so as to be detectable, and an oxide layer that is in contactwith the recording layer. The recording layer contains a Ge—Bi—Te—Mmaterial that is represented by the following formula:Ge_(α)Bi_(β)Te_(γ)M_(100-α-β-γ)(atom %),where M denotes at least one element selected from Al, Ga, In and Mn,and α, β and γ satisfy 25≦α≦60, 0<β≦18, 35≦γ≦55, and 82≦α+β+γ<100. Theoxide layer contains at least one oxide of the element M contained inthe recording layer.

In this description, “atomic %” indicates that the total amount of “Ge”atom, “Bi” atom, “Te” atom and “M” atom is taken as the reference (100%)in the composition formula.

The information recording medium of the present invention is providedwith the recording layer containing a Ge—Bi—Te—M material that has beendeveloped in accordance with the increased speeds of the medium, and theoxide layer containing the oxide of the same element as the element Mcontained in the recording layer. When the oxide layer that is incontact with the recording layer contains an oxide of an element commonwith the element (element M in the present invention) contained in therecording layer as described above, separation between the recordinglayer and the oxide layer can be suppressed effectively. Accordingly, ahighly reliable information recording medium having excellent moistureresistance can be obtained.

A method for manufacturing the information recording medium of thepresent invention is a method for manufacturing an information recordingmedium including a recording layer whose phase can change by an opticalor an electrical system so as to be detectable, and an oxide layer thatis in contact with the recording layer, the method including:

-   (i) forming the recording layer containing a Ge—Bi—Te—M material    represented by the following formula:    Ge_(α)Bi_(β)Te_(γ)M_(100-α-β-γ)(atom %),    where α, β and γ satisfy 25≦α≦60, 0<β≦18, 35≦γ≦55, and 82≦α+β+γ<100,    by a sputtering method using a first sputtering target containing    Ge, Bi, Te, and element M, where M denotes at least one element    selected from Al, Ga, In, and Mn, and-   (ii) forming the oxide layer containing at least one oxide of the    element M contained in the recording layer by a sputtering method    using a second sputtering target containing at least either one    selected from the element M and an oxide of the element M.

An apparatus for manufacturing the information recording medium of thepresent invention is an apparatus to be used for the manufacturingmethod of the present invention mentioned above. The apparatus isprovided with a sputtering device that includes an electrode, the firstsputtering target or the second puttering target, and a substrate holderplaced facing the first sputtering target or the second sputteringtarget.

The method and the apparatus for manufacturing the information recordingmedium of the present invention can provide a highly reliableinformation recording medium as described above.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view of an optical disc as an example of theinformation recording medium of the present invention.

FIG. 2 is a cross-sectional view of an optical disc as another exampleof the information recording medium of the present invention.

FIG. 3 is a schematic view illustrating an example of a sputteringdevice to be used for the apparatus for manufacturing the informationrecording medium of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION Embodiment 1

Hereinafter, an embodiment of the present invention will be describedwith reference to the drawings.

A structure of a disc-like information recording medium used in thisembodiment is described using FIG. 1. In FIG. 1, a laser beam 29 to beused for recording and reproducing information is incident from the sideof a cover layer 15. A disc-like transparent substrate with a smoothsurface is used for a substrate 11. For example, a resin plate made ofpolycarbonate, PMMA (polymethylmethacrylate) or the like and a glassplate can be used. A continuous groove or the like in the form of aspiral or a concentric circle may be formed on a surface of thesubstrate.

A first information layer 12 is formed on the substrate 11. The firstinformation layer 12 has at least a reflective layer 16, a dielectriclayer 17, a recording layer 19, and a dielectric layer 21.

An optical separation layer 13 is formed on the first information layer12. The optical separation layer 13 is composed of a materialtransparent with respect to the wavelength of the laser beam 29 withwhich the first information layer is irradiated in order to record orreproduce signals on and from the first information layer 12. Theoptical separation layer 13 serves to optically separate the firstinformation layer 12 and a second information layer 14. The opticalseparation layer 13 can be produced, for example, by forming a layermade of an ultraviolet curable resin or the like by spin coating, or bybonding a transparent film using an adhesive tape, the ultravioletcurable resin or the like. A continuous groove or the like in the formof a spiral or a concentric circle is formed on a surface of the opticalseparation layer 13.

The second information layer 14 is formed on the optical separationlayer 13. The second information layer 14 has at least a reflectivelayer 23, a dielectric layer 24, a recording layer 26, and a dielectriclayer 28. The cover layer 15 is formed on the second information layer14. The cover layer 15 can be produced, for example, by forming a layermade of an ultraviolet curable resin or the like by spin coating, or bybonding a transparent film onto the second information layer 14 usingthe adhesive tape, the ultraviolet curable resin or the like.

Examples of the material to be used for the dielectric layers 17 and 24include an oxide of Al, Cr, Dy, Ga, Hf, In, Nb, Sn, Y, Zn, Si, Ta, Mo,W, Zr or the like, a sulfide such as ZnS, a nitride of Al, B, Cr, Ge,Si, Ti, Zr, Ta or the like, and a fluoride of Bi, Ce, Dy, Er, Eu La orthe like. As a mixture, ZnS—SiO₂, ZrO₂—SiO₂, ZrO₂—Cr₂O₃,ZrO₂—SiO₂—Cr₂O₃, ZrO₂—Ga₂O₃, ZrO₂—SiO₂—Ga₂O₃, ZrO₂—SiO₂—Cr₂O₃—LaF₃,SnO₂—Ga₂O₃, SnO₂—In₂O₃, ZrO₂—In₂O₃, ZrO₂—SiO₂ —In₂O₃, HfO₂—Cr₂O₃,HfO₂—SiO₂, HfO₂—SiO₂—Cr₂O₃, SnO₂—Nb₂O₃, SnO₂—Si₃N₄ or the like may beused. Preferably, the dielectric layer 17 has a thickness of 10 to 40nm, and more preferably a thickness of 15 to 30 nm from the viewpoint ofdisc reflectance and recording sensitivity. Preferably, the dielectriclayer 24 has a thickness of 5 to 30 nm, and more preferably a thicknessof 10 to 22 nm from the viewpoint of disc reflectance and recordingsensitivity. As ZrO₂, partially stabilized ZrO₂ containing 3 mol % ofY₂O₃ with respect to ZrO₂ (ZrO₂:97 mol %, Y₂O₃:3 mol %), or stabilizedZrO₂ containing 8 mol % of Y₂O₃ (ZrO₂:92 mol %, Y₂O₃:8 mol %) may beused.

Examples of the material to be used for the dielectric layers 21 and 28include an oxide of Al, Cr, Dy, Ga, Hf, In, Nb, Sn, Y, Zn, Si, Ta, Mo,W, Zr or the like, sulfides such as ZnS, a nitride of Al, B, Cr, Ge, Si,Ti, Zr, Ta or the like, and a fluoride of Bi, Ce, Dy, Er, Eu, La or thelike. As a mixture, ZnS—SiO₂, ZrO₂—SiO₂, ZrO₂—Cr₂O₃, ZrO₂—SiO₂—Cr₂O₃,ZrO₂—Ga₂O₃, ZrO₂—SiO₂—Ga₂O₃, ZrO₂—SiO₂—Cr₂O₃—LaF, SnO₂—Ga₂O₃,SnO₂—In₂O₃, ZrO₂—In₂O₃, ZrO₂—SiO₂—In₂O₃, HfO₂—Cr₂O₃, HfO₂—SiO₂,HfO₂—SiO₂—Cr₂O₃, SnO₂—Nb₂O₃, SnO₂—Si₃N₄ or the like may be used.Preferably, the dielectric layer 21 has a thickness of 40 to 80 nm, andmore preferably a thickness of 55 to 75 nm from the viewpoint of discreflectance and recording sensitivity. Preferably, the dielectric layer28 has a thickness of 25 to 50 nm, and more preferably a thickness of 30to 45 nm from the viewpoint of disc reflectance and recordingsensitivity. As ZrO₂, partially stabilized ZrO₂ containing 3 mol % ofY₂O₃ with respect to ZrO₂, or stabilized ZrO₂ containing 8 mol % of Y₂O₃may be used.

In this embodiment, the first information layer 12 is provided with aninterface layer 20 between the dielectric layer 21 and the recordinglayer 19, and an interface layer 18 between the recording layer 19 andthe dielectric layer 17. The second information layer 14 is providedwith an interface layer 27 between the dielectric layer 28 and therecording layer 26, and an interface layer 25 between the recordinglayer 26 and the dielectric layer 24. These interface layers (oxidelayers) provided in contact with the recording layers contain at leastone oxide of an element M contained in the recording layers. The elementM denotes at least one element selected from Al, Ga, In, and Mn, andthis is the same with each element M to be described hereinafter. Whenthe interface layers are formed using such materials, separation betweenthe recording layer and the interface layer can be suppressed, andthereby a highly reliable information recording medium can be obtained.The content of the oxide of the element M in the interface layers ispreferably more than 10 mol % (for example, 12 mol % or higher, or 15mol % or higher), and more preferably 20 mol % or higher. Also, thecontent of the oxide of the element M in the interface layers ispreferably 90 mol % or lower, and more preferably 80 mol % or lower. Theinterface layers may be formed only of the oxide of the element M, andalso may be formed of a mixture of the oxide of the element M and anoxide of another element. As the oxide of another element, at least oneoxide selected from Zr oxide, Si oxide, Cr oxide, Hf oxide, and Y oxidesuitably is used, for example. When a plurality of element M iscontained in the recording layers, the interface layers in contact withthe recording layers contain at least an oxide of one of the pluralityof element M contained in the recording layers. As a mixture,ZrO₂—In₂O₃, ZrO₂—Mn₃O₄, ZrO₂—Al₂O₃, ZrO₂—Ga₂O₃, ZrO₂—SiO₂—Ga₂O₃,ZrO₂—SiO₂—Mn₃O₄, ZrO₂—SiO₂—Al₂O₃, ZrO₂—SiO₂—In₂O₃,ZrO₂—SiO₂—Cr₂O₃—In₂O₃, ZrO₂—SiO₂—Cr₂O₃—Al₂O₃, ZrO₂—SiO₂—Cr₂O₃—Mn₃O₄,ZrO₂—SiO₂—Cr₂O₃—Ga₂O₃, ZrO₂—Y₂O₃—In₂O₃, ZrO₂—Y₂O₃—Al₂O₃,ZrO₂—Y₂O₃—Mn₃O₄, ZrO₂—Y₂O₃—Ga₂O₃, ZrO₂—SiO₂—HfO₂—In₂O₃,ZrO₂—SiO₂—HfO₂—Al₂O₃, ZrO₂—SiO₂—HfO₂—Ga₂O₃, ZrO₂—SiO₂—HfO₂—Mn₃O₄,ZrO₂—Y₂O₃—SiO₂—Ga₂O₃, ZrO₂—Y₂O₃—SiO₂—Mn₃O₄, ZrO₂—Y₂O₃—SiO₂—Al₂O₃,ZrO₂—Y₂O₃—SiO₂—In₂O₃, ZrO₂—Y₂O₃—In₂O₃—Cr₂O₃, ZrO₂—Y₂O₃—Al₂O₃—Cr₂O₃,ZrO₂—Y₂O₃—Mn₃O₄—Cr₂O₃, and ZrO₂—Y₂O₃—Ga₂O₃—Cr₂O₃ may be used, forexample. Preferably, the interface layers 18, 20, 25, and 27 have athickness of 1 to 10 nm, and further preferably have a thickness of 3 to7 nm. As ZrO₂, partially stabilized ZrO₂ containing 3 mol % of Y₂O₃ withrespect to ZrO₂, or stabilized ZrO₂ containing 8 mol % of Y₂O₃ may beused.

Although the interface layer is provided on both sides of each of therecording layers in this embodiment, it is not limited to thisconfiguration. In the first information layer 12, for example, theinterface layer may be provided either between the dielectric layer 21and the recording layer 19 or between the recording layer 19 and thedielectric layer 17. This is also the case with the second informationlayer 14.

The recording layers 19 and 26 of the present invention are formed usinga material containing a phase change material (a Ge—Bi—Te—M material)that contains, as its main component, Te, Ge, Bi, and element M. Sincethe element M is as described above, examples of the material to be usedfor the recording layers 19 and 26 include Ge—Te—Bi—In, Ge—Te—Bi—Al,Ge—Te—Bi—Ga, Ge—Te—Bi—Mn, Ge—Te—Bi—In—Sn, Ge—Te—Bi—Al—Sn,Ge—Te—Bi—Ga—Sn, Ge—Te—Bi—Mn—Sn, Ge—Te—Bi—In—Ag, Ge—Te—Bi—Al—Ag,Ge—Te—Bi—Ga—Ag, Ge—Te—Bi—Mn—Ag, Ge—Te—Bi—In—Au, Ge—Te—Bi—Al—Au,Ge—Te—Bi—Ga—Au, and Ge—Te—Bi—Mn—Au. Specifically, a material whosecomposition is represented by Ge_(α)Bi_(β)Te_(γ)M_(100-α-β-γ) (atom %),where 25≦α60, 0≦β18, 35≦γ≦55, and 82≦α+β+γ<100 is used. The samenumerical value ranges are applied to α, β, and γ to be described below.Preferably, the recording layer 19 has a thickness of 8 to 18 nm fromthe viewpoint of reflectance. Preferably, the recording layer 26 has athickness of 5 to 12 nm from the viewpoint of transmittance.

A material containing, as its main component, metallic elements, such asAg, Au, and Al, can be used for the reflective layers 16 and 23. An Agalloy or an Al alloy obtained by adding elements, such as Mg, Ca, Cr,Nd, Pd, Cu, Ni, Co, Pt, Ga, Dy, In, Nb, V, Ti, La, Bi, Ce, Pr, Sm, Gd,Th, Y, Zn, Mo, W, Ta, Nb, Fe to Ag or Al may be used. Preferably, thereflective layer 16 has a thickness of 50 to 160 nm, and furtherpreferably has a thickness of 60 to 100 nm from the viewpoint ofreflectance. Preferably, the reflective layer 23 has a thickness of 6 to15 nm, and further preferably has a thickness of 7 to 12 nm from theviewpoint of transmittance.

For a high refractive index layer 22, a material containing, as its maincomponent, an oxide of Ti or Nb, a nitride of Ti or Nb, or a mixture ofthese. These materials are characterized in that they have a refractiveindex higher than that of the dielectric layers 17, 21, 24, and 28 andthe interface layers 18, 20, 25, and 27 at a laser beam wavelength of400 nm, at which information is recorded and reproduced. Thereby, ahigher transmission can be realized. For example, TiO₂ has a refractiveindex of 2.7 at a wavelength of 400 nm while ZnS-20 mol % SiO₂ to beused for the dielectric layers has a refractive index of 2.3, andZrO₂-50 mol % In₂O₃ to be used for the interface layers has a refractiveindex of 2.2. Preferably, the high refractive index layer 22 has athickness of 10 to 30 nm, and further preferably has a thickness of 15to 25 nm from the viewpoint of transmittance. “ZnS-20 mol % SiO₂”indicates a mixture of 80 mol % of ZnS and 20 mol % of SiO₂. “ZrO₂-50mol % In₂O₃” indicates a mixture of 50 mol % of ZrO₂ and 50 mol % ofIn₂O₃. That is, in this specification, a mixture of compound A of(100-X) mol % and compound B of X mol % is referred to as “A-X mol % B”or “(A)_((100-X))(B)_(X)” in some cases.

As a method for forming the dielectric layers, the recording layers, thereflective layers, the interface layers, and the high refractive indexlayer, an electron beam vapor deposition method, a sputtering method, aCVD method, a laser sputtering method or the like usually are adopted.The most suitable method, such as DC sputtering and RF sputtering, willbe used according to the sputtering material. Generally, the dielectriclayers and the interface layers are formed by RF sputtering, therecording layers and the reflective layers are formed by DC sputtering,and the high refractive index layer, which the present inventors haveadopted, is formed by DC sputtering. This, however, also depends on thematerial of the target. There may arise a difference between thecomposition of the film formed by sputtering and the composition of thesputtering target due to the sputtering device or the sputteringconditions to be used. However, with the sputtering device and thesputtering conditions that the present inventors have been studying, thecomposition difference hardly occurs. Thus, it is possible to use asputtering target having the same composition as that of the film to beformed in order to obtain a film of desired composition. Accordingly, inorder to form the recording layers 19 and 26 by sputtering, a sputteringtarget (a first sputtering target) having a composition represented byGe_(α)Bi_(β)Te_(γ)M_(100-α-β-γ) (atom %), which is the composition ofthe film to be formed, can be used. Specifically, the recording layers19 and 26 can be formed using a sputtering target that has a compositionsuch as Ge₄₄Bi₄Te₅₁Ga₁ (atom %), Ge₄₄Bi₄Te₅₁Mn₁ (atom %), Ge₄₄Bi₄Te₅₁In₁(atom %), and Ge₄₄Bi₄Te₅₁Al₁ (atom %), for example. In order to form theinterface layers 18, 20, 25, and 27 by sputtering, it is possible, forexample, to use a sputtering target (a second sputtering target) havinga composition obtained by mixing an oxide of the element M contained inthe recording layers 19 and 26 and at least one oxide selected from Zroxide, Si oxide, Cr oxide, Hf oxide, and Y oxide. Specifically, asputtering target having a composition such as ZrO₂-50 mol % In₂O₃,ZrO₂-50 mol % Al₂O₃, ZrO₂-50 mol % Mn₃O₄ and ZrO₂-50 mol % Ga₂O₃ can beused, for example. As a sputtering gas necessary for sputtering, aninert gas typified by Ar may be used. Furthermore, oxygen, nitrogen orthe like may be used as an additive gas.

As an apparatus for manufacturing the information recording medium ofthe present invention, it is possible, for example, to use amanufacturing apparatus provided with a sputtering device that includesan electrode, the first sputtering target or the second sputteringtarget, and a substrate holder placed facing one of these sputteringtargets. The use of such an apparatus makes it possible to form therecording layers and the interface layers constituting the informationrecording medium of the present invention on a substrate disposed on thesubstrate holder. FIG. 3 illustrates one example of the sputteringdevice. The sputtering device to be used for forming the informationrecording medium of the present invention is not limited to this. Asshown in FIG. 3, this sputtering device is designed so that a vacuumpump (not shown) can be connected to a vacuum chamber 31 via an air exitport 32 in order to maintain the interior of the vacuum chamber 31 undera high vacuum. A constant flow of gas can be supplied from a gas supplyport 33. A substrate 35 (the substrate referred to herein means asubstrate on which films to be stacked) is mounted on an anode(electrode, substrate holder) 34. By grounding the vacuum chamber 31,the vacuum chamber 31 and the substrate 35 are maintained anodic. Asputtering target 36 is connected to a cathode (electrode) 37 and isconnected to a power supply via a switch (not shown). Application of apredetermined voltage between the anode 34 and the cathode 37 causesejection of particles from the sputtering target 36, and the particlesform a thin film on the substrate 35.

This embodiment describes an information recording medium in which thetwo information layers 12 and 14 are stacked with the optical separationlayer 13 interposed therebetween. However, even in the case where onlyone information layer is provided (in the case where only the substrate1, the first information layer 2 and the cover layer 9 are provided, oronly the substrate 1, the second information layer 4, and the coverlayer 9 are provided in FIG. 1), the same effect can be obtained byusing the same materials as those described in this embodiment for therecording layer and the interface layers. Furthermore, in the case of aninformation recording medium provided with three or more informationlayers as shown in FIG. 2, the same effect also can be obtained by usingthe same materials as those described in this embodiment for therecording layer and the interface layer in at least one of theinformation layers.

EXAMPLES

Hereinafter, the present invention is described in further detail usingexamples.

Comparative Example 1

A structure of a disc-like information recording medium of comparativeexample 1 is described in detail with reference to FIG. 1 and Table 1. Apolycarbonate substrate with a diameter of 120 mm and a thickness of 1.1mm having on its surface a concave-convex guide groove with a pitch of0.3 μm and a depth of 20 nm was used as the substrate 11. A 100-nm-thickAg alloy film to serve as the reflective layer 16, a 25-nm-thick ZrO₂-20mol % Cr₂O₃ film to serve as the dielectric layer 17, a 12-nm-thickGe₄₄Bi₄Te₅₁Ga₁ film to serve as the recording layer 19, a 5-nm-thickZrO₂-20 mol % Cr₂O₃ film to serve as the interface layer 20, and a65-nm-thick ZnS-20 mol % SiO₂ film to serve as the dielectric layer 21were formed respectively on the substrate by a magnetron sputteringmethod to form the first information layer 12. In this case, theinterface layer 18 shown in FIG. 1 is omitted. Then, an ultravioletcurable resin was applied on the first information layer 12, and apolycarbonate substrate with a radius of 120 mm and a thickness of 0.6mm having on its surface a concave-convex guide groove with a pitch of0.3 μm and a depth of 20 nm was allowed to adhere thereto. Theultraviolet curable resin was cured by ultraviolet ray irradiation, andthe polycarbonate substrate was stripped off. Thus the opticalseparation layer 13 of 25 μm thickness with a groove transferred to itssurface was formed. Subsequently, a 24-nm-thick TiO₂ film to serve asthe high refractive index layer 22, an 10-nm-thick Ag alloy film toserve as the reflective layer 23, which has the same materialcomposition as that of the reflective layer 16 of the first informationlayer, a 18-nm-thick ZrO₂-20 mol % Cr₂O₃ film to serve as the dielectriclayer 24, a 7-nm-thick Ge₄₄Bi₄Te₅₁Ga₁ film to serve as the recordinglayer 26, a 5-nm-thick ZrO₂-20 mol % Cr₂O₃ film to serve as theinterface layer 27, a 35-nm-thick ZnS-20 mol % SiO₂ film to serve as thedielectric layer 28 were formed respectively on the optical separationlayer 13 by the magnetron sputtering method to form the secondinformation layer 14. Then, the cover layer 15 with a thickness of 0.1mm was formed by a spin coat method. In short, the information recordingmedium of Comparative Example 1 describes the case where any oxides ofthe elements contained in the recording layers are not contained in theinterface layers corresponding to the oxide layers of the presentinvention.

TABLE 1 Material composition of the first information layer 12Reflective Ag alloy layer 16 Dielectric ZrO₂ ₋ 20 mol layer 17 % Cr₂O₃Interface Not provided layer 18 Recording Ge₄₄Bi₄Te₅₁Ga₁ layer 19Interface ZrO₂ ₋ 20 mol layer 20 % Cr₂O₃ Dielectric ZnS-20 mol layer 21% SiO₂ Material composition of the second information layer 14 High TiO₂refractive index layer 22 Reflective Ag alloy layer 23 Dielectric ZrO₂ ₋20 mol layer 24 % Cr₂O₃ Interface Not provided layer 25 RecordingGe₄₄Bi₄Te₅₁Ga₁ layer 26 Interface ZrO₂ ₋ 20 mol layer 27 % Cr₂O₃Dielectric ZnS-20 mol layer 28 % SiO₂

Comparative Example 2

A structure of a disc-like information recording medium of comparativeexample 2 is described in detail with reference to FIG. 1 and Table 2. Apolycarbonate substrate with a diameter of 120 mm and a thickness of 1.1mm having on its surface a concave-convex guide groove with a pitch of0.3 μm and a depth of 20 nm was used as the substrate 11. A 80-nm-thickAg alloy film to serve as the reflective layer 16, a 20-nm-thick ZrO₂-20mol % Cr₂O₃ film to serve as the dielectric layer 17, a 5-nm-thickZrO₂-25 mol % SiO₂-50 mol % Ga₂O₃ film to serve as the interface layer18, a 12-nm-thick Ge₄₄Bi₄Te₅₁Al₁ film to serve as the recording layer19, a 5-nm-thick ZrO₂-25 mol % SiO₂-50 mol % Ga₂O₃ film to serve as theinterface layer 20, and a 65-nm-thick ZnS-20 mol % SiO₂ film to serve asthe dielectric layer 21 were formed respectively on the substrate by themagnetron sputtering method to form the first information layer 12.Then, an ultraviolet curable resin was applied on the first informationlayer 12, and a polycarbonate substrate with a radius of 120 mm and athickness of 0.6 mm having on its surface a concave-convex guide groovewith a pitch of 0.3 μm and a depth of 20 nm was allowed to adherethereto. The ultraviolet curable resin was cured by ultraviolet rayirradiation, and the polycarbonate substrate was stripped off. Thus theoptical separation layer 13 of 25 μm thickness with a groove transferredto its surface was formed. Subsequently, a 23-nm-thick TiO₂ film toserve as the high refractive index layer 22, a 10-nm-thick Ag alloy filmto serve as the reflective layer 23, which has the same materialcomposition as that of the reflective layer 24 of the first informationlayer 12, a 13-nm-thick ZrO₂-20 mol % Cr₂O₃ film to serve as thedielectric layer 24, a 5-nm-thick ZrO₂-25 mol % SiO₂-50 mol % Ga₂O₃ filmto serve as the interface layer 25, a 7-nm-thick Ge₄₄Bi₄Te₅₁Al₁ film toserve as the recording layer 26, a 5-nm-thick ZrO₂-25 mol % SiO₂-50 mol% Ga₂O₃ film to serve as the interface layer 27, and a 35-nm-thickZnS-20 mol % SiO₂ film to serve as the dielectric layer 28 were formedrespectively on the optical separation layer 13 by the magnetronsputtering method to form the second information layer 14. Then, thecover layer 15 with a thickness of 0.1 mm was formed by the spin coatmethod. In short, the information recording medium of ComparativeExample 2 describes the case where no oxides of the elements containedin the recording layers are contained in the interface layerscorresponding to the oxide layers of the present invention.

TABLE 2 Material composition of the first information layer 12Reflective Ag alloy layer 16 Dielectric ZrO₂ ₋ 20 mol layer 17 % Cr₂O₃Interface ZrO₂ ₋ 25 mol Layer 18 % SiO₂ ₋ 50 mol % Ga₂O₃ RecordingGe₄₄Bi₄Te₅₁Al₁ layer 19 Interface ZrO₂ ₋ 25 mol layer 20 % SiO₂ ₋ 50 mol% Ga₂O₃ Dielectric ZnS-20 mol layer 21 % SiO₂ Material composition ofthe second information layer 14 High TiO₂ refractive index layer 22Reflective Ag alloy layer 23 Dielectric ZrO₂ ₋ 20 mol layer 24 % Cr₂O₃Interface ZrO₂ ₋ 25 mol layer 25 % SiO₂ ₋ 50 mol % Ga₂O₃ RecordingGe₄₄Bi₄Te₅₁Al₁ layer 26 Interface ZrO₂ ₋ 25 mol layer 27 % SiO₂ ₋ 50 mol% Ga₂O₃ Dielectric ZnS-20 mol layer 28 % SiO₂

Example 1

A structure of a disc-like information recording medium of Example 1 isdescribed in detail with reference to FIG. 1 and Table 3. Apolycarbonate substrate with a diameter of 120 mm and a thickness of 1.1mm having on its surface a concave-convex guide groove with a pitch of0.3 μm and a depth of 20 nm was used as the substrate 11. A 80-nm-thickAg alloy film to serve as the reflective layer 16, a 20-nm-thick ZrO₂-20mol % Cr₂O₃ film to serve as the dielectric layer 17, a 5-nm-thickZrO₂-25 mol % SiO₂-50 mol % Ga₂O₃ film to serve as the interface layer18, a 12-nm-thick Ge₄₄Bi₄Te₅₁Ga₁ film to serve as the recording layer19, a 5-nm-thick ZrO₂-25 mol % SiO₂-50 mol % Ga₂O₃ film to serve as theinterface layer 20, and a 65-nm-thick ZnS-20 mol % SiO₂ film to serve asthe dielectric layer 21 were formed respectively on the substrate by themagnetron sputtering method to form the first information layer 12.Then, an ultraviolet curable resin was applied on the first informationlayer 12, and a polycarbonate substrate with a radius of 120 mm and athickness of 0.6 mm having on its surface a concave-convex guide groovewith a pitch of 0.3 μm and a depth of 20 nm was allowed to adherethereto. The ultraviolet curable resin was cured by ultraviolet rayirradiation, and the polycarbonate substrate was stripped off. Thus theoptical separation layer 13 of 25 μm thickness with a groove transferredto its surface was formed. Subsequently, a 23-nm-thick TiO₂ film toserve as the high refractive index layer 22, a 10-nm-thick Ag alloy filmto serve as the reflective layer 23, which has the same materialcomposition as that of the reflective layer 24 of the first informationlayer, a 13-nm-thick ZrO₂-20 mol % Cr₂O₃ film to serve as the dielectriclayer 25, a 5-nm-thick ZrO₂-25 mol % SiO₂-50 mol % Ga₂O₃ film to serveas the interface layer 26, a 7-nm-thick Ge₄₄Bi₄Te₅₁Ga₁ film to serve asthe recording layer 27, a 5-nm-thick ZrO₂-25 mol % SiO₂-50 mol % Ga₂O₃film to serve as the interface layer 28, and a 35-nm-thick ZnS-20 mol %SiO₂ film to serve as the dielectric layer 29 were formed respectivelyon the optical separation layer 13 by the magnetron sputtering method toform the second information layer 14. Then, the cover layer 15 with athickness of 0.1 mm was formed by the spin coat method. In short, theinformation recording medium of Example 1 describes the case where anoxide of at least one of the elements contained in the recording layersis contained in the interface layers (Ga in the recording layers andGa₂O₃ in the interface layers).

TABLE 3 Material composition of the first information layer 12Reflective Ag alloy layer 16 Dielectric ZrO₂ ₋ 20 mol layer 17 % Cr₂O₃Interface ZrO₂ ₋ 25 mol Layer 18 % SiO₂ ₋ 50 mol % Ga₂O₃ RecordingGe₄₄Bi₄Te₅₁Ga₁ layer 19 Interface ZrO₂ ₋ 25 mol layer 20 % SiO₂ ₋ 50 mol% Ga₂O₃ Dielectric ZnS-20 mol layer 21 % SiO₂ Material composition ofthe second information layer 14 High TiO₂ refractive index layer 22Reflective Ag alloy layer 23 Dielectric ZrO₂ ₋ 20 mol layer 24 % Cr₂O₃Interface ZrO₂ ₋ 25 mol layer 25 % SiO₂ ₋ 50 mol % Ga₂O₃ RecordingGe₄₄Bi₄Te₅₁Ga₁ layer 26 Interface ZrO₂ ₋ 25 mol layer 27 % SiO₂ ₋ 50 mol% Ga₂O₃ Dielectric ZnS-20 mol layer 28 % SiO₂

Example 2

A structure of a disc-like information recording medium of Example 2 isdescribed in detail with reference to FIG. 1 and Table 4. Apolycarbonate substrate with a diameter of 120 mm and a thickness of 1.1mm having on its surface a concave-convex guide groove with a pitch of0.3 μm and a depth of 20 nm was used as the substrate 11. A 80-nm-thickAg alloy film to serve as the reflective layer 16, a 20-nm-thick ZrO₂-20mol % Cr₂O₃ film to serve as the dielectric layer 17, a 5-nm-thickZrO₂-20 mol % Ga₂O₃ film (X varies in a range of 0≦X≦90) to serve as theinterface layer 18, a 12-nm-thick Ge₄₄Bi₄Te₅₁Ga₁ film to serve as therecording layer 19, a 5-nm-thick ZrO₂—X mol % Ga₂O₃ film (X varies in arange of 0≦X≦90) to serve as the interface layer 20, and a 65-nm-thickZnS-20 mol % SiO₂ film to serve as the dielectric layer 21 were formedrespectively on the substrate by the magnetron sputtering method to formthe first information layer 12. Then, an ultraviolet curable resin wasapplied on the first information layer 12, and a polycarbonate substratewith a radius of 120 mm and a thickness of 0.6 mm having on its surfacea concave-convex guide groove with a pitch of 0.3 μm and a depth of 20nm was allowed to adhere thereto. The ultraviolet curable resin wascured by ultraviolet ray irradiation, and the polycarbonate substratewas stripped off. Thus the optical separation layer 13 of 25 μmthickness with a groove transferred to its surface was formed.Subsequently, a 23-nm-thick TiO₂ film to serve as the high refractiveindex layer 22, a 10-nm-thick Ag alloy film to serve as the reflectivelayer 23, which has the same material composition as that of thereflective layer 16 of the first information layer 12, a 13-nm-thickZrO₂-20 mol % Cr₂O₃ film to serve as the dielectric layer 24, a5-nm-thick ZrO₂—X mol % Ga₂O₃ film (X varies in a range of 0≦X≦90) toserve as the interface layer 25, a 7-nm-thick Ge₄₄Bi₄Te₅₁Ga₁ film toserve as the recording layer 26, a 5-nm-thick ZrO₂—X mol % Ga₂O₃ film (Xvaries in a range of 0≦X≦90) to serve as the interface layer 27, and a35-nm-thick ZnS-20 mol % SiO₂ film to serve as the dielectric layer 28,were formed respectively on the optical separation layer 13 by themagnetron sputtering method to form the second information layer 14.Then, the cover layer 15 with a thickness of 0.1 mm was formed by thespin coat method. In short, the information recording medium of Example2 describes the case where an oxide of at least one of the elementscontained in the recording layers is contained in the interface layers(Ga in the recording layers and Ga₂O₃ in the interface layers). In thisexample, the content (the value of X) of Ga₂O₃ in the interface layers18, 20, 25, and 27 was changed to 0, 10, 12, 15, 20, 30, 40, 50, 60, 70,80 and 90 in terms of mol % to prepare 12 kinds of samples (samples 2-1to 2-12) for studying the composition dependency of the interfacelayers.

TABLE 4 Material composition of the first information layer 12Reflective Ag alloy layer 16 Dielectric ZrO₂ ₋ 20 mol layer 17 % Cr₂O₃Interface ZrO₂ ₋ X mol layer 18 % Ga₂O₃ (X varies in a range of 0 ≦ X ≦90) Recording Ge₄₄Bi₄Te₅₁Ga₁ layer 19 Interface ZrO₂ ₋ X mol layer 20 %Ga₂O₃ (X varies in a range of 0 ≦ X ≦ 90) Dielectric ZnS-20 mol layer 21% SiO₂ Material composition of the second information layer 14 High TiO₂refractive index layer 22 Reflective Ag alloy layer 23 Dielectric ZrO₂ ₋20 mol layer 24 % Cr₂O₃ Interface ZrO₂ ₋ X mol layer 25 % Ga₂O₃ (Xvaries in a range of 0 ≦ X ≦ 90) Recording Ge₄₄Bi₄Te₅₁Ga₁ layer 26Interface ZrO₂ ₋ X mol layer 27 % Ga₂O₃ (X varies in a range of 0 ≦ X ≦90) Dielectric ZnS-20 mol layer 28 % SiO₂

Example 3

A structure of a disk-like information recording medium of Example 3 isdescribed in detail with reference to FIG. 1 and Table 5. Apolycarbonate substrate with a diameter of 120 mm and a thickness of 1.1mm having on its surface a concave-convex guide groove with a pitch of0.3 μm and a depth of 20 nm was used as the substrate 11. A 80-nm-thickAg alloy film to serve as the reflective layer 16, a ZrO₂-20 mol % Cr₂O₃film to serve as the dielectric layer 17, a 5-nm-thick ZrO₂-[(100−X)/2]mol % SiO₂—X mol % In₂O₃ film (X varies in a range of 0≦X≦90) to serveas the interface layer 18, a 12-nm-thick Ge₄₄Bi₄Te₅₁In₁ film to serve asthe recording layer 19, a 5-nm-thick ZrO₂-[(100−X)/2] mol % SiO₂—X mol %In₂O₃ film (X varies in a range of 0≦X≦90) to serve as the interfacelayer 20, and a 65-nm-thick ZnS-20 mol % SiO₂ film to serve as thedielectric layer 21 were formed respectively on the substrate by themagnetron sputtering method to form the first information layer 12.Then, an ultraviolet curable resin was applied on the first informationlayer 12, and a polycarbonate substrate with a radius of 120 mm and athickness of 0.6 mm having on its surface a concave-convex guide groovewith a pitch of 0.3 μm and a depth of 20 nm was allowed to adherethereto. The ultraviolet curable resin was cured by ultraviolet rayirradiation, and the polycarbonate substrate was stripped off. Then theoptical separation layer 13 of 25 μm thickness with a groove transferredto its surface was formed. Subsequently, a 23-nm-thick TiO₂ film toserve as the high refractive index layer 22, a 10-nm-thick Ag alloy filmto serve as the reflective layer 23, which has the same materialcomposition as that of the reflective layer 16 of the first informationlayer 12, a 13-nm-thick ZrO₂-20 mol % Cr₂O₃ film to serve as thedielectric layer 24, a 5-nm-thick ZrO₂-[(100−X)/2] mol % SiO₂—X mol %In₂O₃ (X varies in a range of 0≦X≦90) film to serve as the interfacelayer 25, a 7-nm-thick Ge₄₄Bi₄Te₅₁In₁ film to serve as the recordinglayer 26, a 5-nm-thick ZrO₂-[(100−X)/2] mol % SiO₂—X mol % In₂O₃ (Xvaries in a range of 0≦X≦90) film to serve as the interface layer 27,and a 35-nm-thick ZnS-20 mol % SiO₂ film to serve as the dielectriclayer 28, were formed respectively on the optical separation layer 13 bythe magnetron sputtering method to form the second information layer 14.Then, the cover layer 15 with a thickness of 0.1 mm was formed by thespin coat method. In short, the information recording medium of Example3 describes the case where an oxide of at least one of the elementscontained in the recording layers is contained in the interface layers(In the recording layers and In₂O₃ in the interface layers). In thisexample, the content (the value of X) of In₂O₃ in the interface layers18, 20, 25, and 27 was changed to 0, 10, 12, 15, 20, 30, 40, 50, 60, 70,80 and 90 in terms of mol % to prepare 12 kinds of samples (samples 3-1to 3-12) for studying composition dependency of the interface layers.

TABLE 5 Material composition of the first information layer 12Reflective Ag alloy layer 16 Dielectric ZrO₂ ₋ 20 mol layer 17 % Cr₂O₃Interface ZrO₂-[(100 − X)/ layer 18 2] mol % SiO₂ ₋ X mol % In₂O₃ (Xvaries in a range of 0 ≦ X ≦ 90) Recording Ge₄₄Bi₄Te₅₁In₁ layer 19Interface ZrO₂ ₋ [(100 − X)/ layer 20 2] mol % SiO₂ ₋ X mol % In₂O₃ (Xvaries in a range of 0 ≦ X ≦ 90) Dielectric ZnS-20 mol layer 21 % SiO₂Material composition of the second information layer 14 High TiO₂refractive index layer 22 Reflective Ag alloy layer 23 Dielectric ZrO₂ ₋20 mol layer 24 % Cr₂O₃ Interface ZrO₂ ₋ [(100 − X)/ layer 25 2] mol %SiO₂ ₋ X mol % In₂O₃ (X varies in a range of 0 ≦ X ≦ 90) RecordingGe₄₄Bi₄Te₅₁In₁ layer 26 Interface ZrO₂ ₋ [(100 − X)/ layer 27 2] mol %SiO₂ ₋ X mol % In₂O₃ (X varies in a range of 0 ≦ X ≦ 90) DielectricZnS-20 mol layer 28 % SiO₂

Example 4

A structure of a disk-like information recording medium of Example 4 isdescribed in detail with reference to FIG. 1 and Table 6. Apolycarbonate substrate with a diameter of 120 mm and a thickness of 1.1mm having on its surface a concave-convex guide groove with a pitch of0.3 μm and a depth of 20 nm was used as the substrate 11. A 80-nm-thickAg alloy film to serve as the reflective layer 16, a 20-nm-thick ZrO₂-20mol % Cr₂O₃ film to serve as the dielectric layer 17, a 5-nm-thick[46(ZrO₂)-4(Y₂O₃)]-[(100−X)/2] mol % SiO₂—X mol % In₂O₃ (X varies in arange of 0≦X≦90) film to serve as the interface layer 18, a 12-nm-thickGe₄₄Bi₄Te₅₁In₁ film to serve as the recording layer 19, a 5-nm-thick[46(ZrO₂)-4(Y₂O₃)]-[(100−X)/2] mol % SiO₂—X mol % In₂O₃ (X varies in arange of 0≦X≦90) film to serve as the interface layer 20, and a65-nm-thick ZnS-20 mol % SiO₂ film to serve as the dielectric layer 21,were formed respectively on the substrate by a magnetron sputteringmethod to form the first information layer 12. Then, an ultravioletcurable resin was applied on the first information layer 12, and apolycarbonate substrate with a radius of 120 mm and a thickness of 0.6mm having on its surface a concave-convex guide groove with a pitch of0.3 μm and a depth of 20 nm was allowed to adhere thereto. Theultraviolet curable resin was cured by ultraviolet ray irradiation, andthe polycarbonate substrate was stripped off. Thus the opticalseparation layer 13 of 25 μm thickness with a groove transferred to itssurface was formed. Subsequently, a 23-nm-thick TiO₂ film to serve asthe high refractive index layer 22 of the second information layer 14, a10-nm-thick Ag alloy film to serve as the reflective layer 23, which hasthe same material composition as that of the reflective layer 16 of thefirst information layer 12, a 13-nm-thick ZrO₂-20 mol % Cr₂O₃ film toserve as the dielectric layer 24, a 5-nm-thick[46(ZrO₂)-4(Y₂O₃)]-[(100−X)/2] mol % SiO₂—X mol % In₂O₃ (X varies in arange of 0≦X≦90) film to serve as the interface layer 25, a 7-nm-thickGe₄₄Bi₄Te₅₁In₁ film to serve as the recording layer 26, a 5-nm-thick[46(ZrO₂)-4(Y₂O₃)]-[(100−X)/2] mol % SiO₂—X mol % In₂O₃ (X varies in arange of 0≦X≦90) film to serve as the interface layer 27, and a35-nm-thick ZnS-20 mol % SiO₂ film to serve as the dielectric layer 28,were formed respectively on the optical separation layer 13 by themagnetron sputtering method to form the second information layer 14.Subsequently, the cover layer 15 with a thickness of 0.1 mm was formedby the spin coat method. In short, the information recording medium ofExample 4 describes the case where an oxide of at least one of theelements contained in the recording layers is contained in the interfacelayers (In the recording layers and In₂O₃ in the interface layers). Inthis example, the content (the value of X) of In₂O₃ in the interfacelayers 18, 20, 25, and 27 was changed to 0, 10, 12, 15, 20, 30, 40, 50,60, 70, 80 and 90 in terms of mol % to prepare 12 kinds of samples(samples 4-1 to 4-12) for studying composition dependency of theinterface layers.

TABLE 6 Material composition of the first information layer 12Reflective Ag alloy layer 16 Dielectric ZrO₂ ₋ 20 mol layer 17 % Cr₂O₃Interface [46(ZrO₂)-4(Y₂O₃)]-[(100 − X)/ layer 18 2] mol % SiO₂ ₋ X mol% In₂O₃ (X varies in a range of 0 ≦ X ≦ 90) Recording Ge₄₄Bi₄Te₅₁In₁layer 19 Interface [46(ZrO₂)-4(Y₂O₃)]-[(100 − X)/ layer 20 2] mol % SiO₂₋ X mol % In₂O₃ (X varies in a range of 0 ≦ X ≦ 90) Dielectric ZnS-20mol layer 21 % SiO₂ Material composition of the second information layer14 High TiO₂ refractive index layer 22 Reflective Ag alloy layer 23Dielectric ZrO₂ ₋ 20 mol layer 24 % Cr₂O₃ Interface[46(ZrO₂)-4(Y₂O₃)]-[(100 − X)/ layer 25 2] mol % SiO₂ ₋ X mol % In₂O₃ (Xvaries in a range of 0 ≦ X ≦ 90) Recording Ge₄₄Bi₄Te₅₁In₁ layer 26Interface [46(ZrO₂)-4(Y₂O₃)]-[(100 − X)/ layer 27 2] mol % SiO₂ ₋ X mol% In₂O₃ (X varies in a range of 0 ≦ X ≦ 90) Dielectric ZnS-20 mol layer28 % SiO₂

The discs of Example 1, Comparative Examples 1 and 2 were observed forfilm corrosion (separation) using an optical microscope after it hadbeen left in an environment at 90° C. and a relative humidity of 80%. Anevaluation was made by counting the number of corroded points per fieldof view of the optical microscope after the discs had been left in anenvironment at 90° C. and a relative humidity of 80% for 100 hours. Itis desirable that the number of corroded points is smaller, with zero asa target, in order to meet the requirement that the discs should, as acommercial product, have a lifetime of 30 years at room temperature. Theobservation for the film corrosion was carried out after 50 hours and200 hours as well. Differences in durability also were compared.Needless to say, the less the corrosion occurs, the more reliable thedisc is in a longer period of time of testing. The present inventorsalso aimed at it accordingly. In light of this, not only the number ofcorroded points observed after 100 hours but also that observed after200 hours was taken into consideration. For example, even if corrosionwas observed after 100 hours, it can be judged that the effect ofsuppressing film separation has been obtained when the number ofcorroded points was

The results of the film corrosion test on the discs of Example 1,Comparative Examples 1 and 2 are shown in Table 7 (results of the firstinformation layer) and Table 8 (results of the second informationlayer).

TABLE 7 Comparative Comparative First information layer Example 1Example 2 Example 1 Number of corroded points 0 0 0 after 50 hours in acorrosion test (at 90° C., 80% of relative humidity) Number of corrodedpoints 10 5 0 after 100 hours in a corrosion test (at 90° C., 80% ofrelative humidity) Number of corroded points >50 30 0 after 200 hours ina corrosion test (at 90° C., 80% of relative humidity)

TABLE 8 Comparative Comparative First information layer Example 1Example 2 Example 1 Number of corroded points 5 1 0 after 50 hours in acorrosion test (at 90° C., 80% of relative humidity) Number of corrodedpoints 30 5 0 after 100 hours in a corrosion test (at 90° C., 80% ofrelative humidity) Number of corroded points >50 20 0 after 200 hours ina corrosion test (at 90° C., 80% of relative humidity)

When a Ge—Bi—Te—M material (Ga was selected as M in this comparativeexample) represented by Ge_(α)Bi_(β)Te_(γ)M_(100-α-β-γ) (atom %) wasused while oxide layers containing an oxide of the element M were notused as the interface layers as described in Comparative Example 1,corrosion (separation) was observed after 100 hours on the firstinformation layer and after 50 hours on the second information layer inthe film corrosion test as shown in Table 7 and Table 8. When aGe—Bi—Te—M material (Al was selected as M in this comparative example)represented by Ge_(α)Bi_(β)Te_(γ)M_(100-α-β-γ) (atom %) was used, andoxide layers containing an oxide of the element M (Ga is selected as Min this comparative example) that is not contained in the recordinglayers were used as the interface layers as described in ComparativeExample 2, corrosion (separation) occurred after 100 hours on the firstinformation layer and after 50 hours on the second information layerbecause the element M contained in the recording layers and the elementM contained in the interface layers are different from each other. Asharp increase was observed in the number of corroded points after 200hours with respect to the number of corroded points after 100 hours.

On the other hand, when a Ge—Bi—Te—M material (Ga was selected as M inthis comparative example) represented by Ge_(α)Bi_(β)Te_(γ)M_(100-α-β-γ)(atom %) was used while oxide layers containing an oxide of the elementM (Ga is selected as M in this example) were used as the interfacelayers as described in Example 1, that is, when an oxide of the sameelement as the element M contained in the recording layers is containedin the interface layers, a highly reliable information recording mediumwas obtained that did not have corrosion (separation) until after 200hours in the film corrosion test.

Here, when the element M contained in the recording layers and the oxideof the element M contained in the interface layers are the sameelements, it is effective for improving corrosion resistance. The reasonfor this is not clearly understood, but the present inventors think asfollows. Since the recording layer contained the same element as thatcontained in the interface layer, these elements were slightly mixedbetween the recording layer and the interface layer, connecting therecording layer and the interface layer at the element level, andthereby adhesiveness between the recording layer and the interface layerwas improved. In addition, since the element M contained in theinterface layer is the same as the element M contained in the recordinglayer, even when the element M contained in the interface layer movesinto the recording layer at the time of use, rapid characteristicdegradation hardly occurs with the recording layer because the element Mis an element already contained in the recording layer. In short, theinformation recording medium of the present invention conceivably allowsthe characteristic degradation to be suppressed even after long-termuse.

Next, the results of studies about the relationship between reliabilityand the content of the oxide of the element M in the interface layers ofExample 2 are shown in Table 9 (results of the first information layer)and Table 10 (results of the second information layer).

TABLE 9 (First information layer) Content of the oxide of element M (mol%) 0 10 12 15 20 30 40 50 60 70 80 90 Number of 0 0 0 0 0 0 0 0 0 0 0 0corroded points after 50 hours in a corrosion test (at 90° C., 80% ofrelative humidity) Number of 20 10 5 2 0 0 0 0 0 0 0 1 corroded pointsafter 100 hours in a corrosion test (at 90° C., 80% of relativehumidity) Number of >50 20 10 5 5 0 0 0 0 0 3 5 corroded points after200 hours in a corrosion test (at 90° C., 80% of relative humidity)

TABLE 10 (Second information layer) Content of the oxide of element M(mol %) 0 10 12 15 20 30 40 50 60 70 80 90 Number of 20 5 0 0 0 0 0 0 00 0 0 corroded points after 50 hours in a corrosion test (at 90° C., 80%of relative humidity) Number of >50 25 5 0 0 0 0 0 0 0 0 10 corrodedpoints after 100 hours in a corrosion test (at 90° C., 80% of relativehumidity) Number of >50 >50 >50 >50 >50 20 0 0 0 5 10 20 corroded pointsafter 200 hours in a corrosion test (at 90° C., 80% of relativehumidity)

The results of studies about the relationship between reliability andthe content of the oxide of the element M in the interface layers ofExample 3 are shown in Table 11 (results of the first information layer)and Table 12 (results of the second information layer).

TABLE 11 (First information layer) Content of the oxide of element M(mol %) 0 10 12 15 20 30 40 50 60 70 80 90 Number of 0 0 0 0 0 0 0 0 0 00 0 corroded points after 50 hours in a corrosion test (at 90° C., 80%of relative humidity) Number of 20 10 5 2 0 0 0 0 0 0 0 3 corrodedpoints after 100 hours in a corrosion test (at 90° C., 80% of relativehumidity) Number of >50 20 10 5 7 0 0 0 0 0 5 10 corroded points after200 hours in a corrosion test (at 90° C., 80% of relative humidity)

TABLE 12 (Second information layer) Content of the oxide of element M(mol %) 0 10 12 15 20 30 40 50 60 70 80 90 Number of 20 5 0 0 0 0 0 0 00 0 0 corroded points after 50 hours in a corrosion test (at 90° C., 80%of relative humidity) Number of >50 25 5 0 0 0 0 0 0 0 0 10 corrodedpoints after 100 hours in a corrosion test (at 90° C., 80% of relativehumidity) Number of >50 >50 >50 >50 >50 25 0 0 0 7 15 20 corroded pointsafter 200 hours in a corrosion test (at 90° C., 80% of relativehumidity)

The results of studies about the relationship between reliability andthe content of the oxide of the element M in the interface layers ofExample 4 are shown in Table 13 (results of the first information layer)and Table 14 (results of the second information layer).

TABLE 13 (First information layer) Content of the oxide of element M(mol %) 0 10 12 15 20 30 40 50 60 70 80 90 Number of 0 0 0 0 0 0 0 0 0 00 0 corroded points after 50 hours in a corrosion test (at 90° C., 80%of relative humidity) Number of 20 15 5 3 0 0 0 0 0 0 0 3 corrodedpoints after 100 hours in a corrosion test (at 90° C., 80% of relativehumidity) Number of >50 20 15 7 10 0 0 0 0 0 5 10 corroded points after200 hours in a corrosion test (at 90° C., 80% of relative humidity)

TABLE 14 (Second information layer) Content of the oxide of element M(mol %) 0 10 12 15 20 30 40 50 60 70 80 90 Number of 20 10 0 0 0 0 0 0 00 0 0 corroded points after 50 hours in a corrosion test (at 90° C., 80%of relative humidity) Number of >50 30 10 5 0 0 0 0 0 0 0 15 corrodedpoints after 100 hours in a corrosion test (at 90° C., 80% of relativehumidity) Number of >50 >50 >50 >50 >50 25 0 0 0 7 10 20 corroded pointsafter 200 hours in a corrosion test (at 90° C., 80% of relativehumidity)

As shown in Table 9, in the first information layer of Example 2, it wasproved that when the oxide (Ga₂O₃) of the element M was contained in theinterface layers, the number of corroded points was reduced, and thenumber of corroded points did not sharply increase even after longhours, and further, the number of corroded points was able to be reducedmore reliably when Ga₂O₃ exceeding 10 mol % was contained. Furthermore,it was proved that when the interface layers had a composition of ZrO₂—Xmol % Ga₂O₃ (20≦X≦80 mol %), corrosion (separation) was not observedafter 100 hours in the film corrosion test (at 90° C., 80% of relativehumidity). When the interface layers had a composition of ZrO₂—X mol %Ga₂O₃ (20≦X≦70 mol %), it was proved that corrosion (separation) was notobserved even after 200 hours in the film corrosion test (at 90° C., 80%of relative humidity).

As shown in Table 10, in the second information layer of Example 2, whenthe interface layers had a composition of ZrO₂—X mol % Ga₂O₃ (20≦X≦80),corrosion (separation) was not observed after 100 hours in the filmcorrosion test (at 90° C., 80% of relative humidity). When the interfacelayers had a composition of ZrO₂—X mol % Ga₂O₃ (40≦X≦60), corrosion(separation) was not observed after 200 hours in a film corrosion test(at 90° C., 80% of relative humidity).

As shown in Table 11, in the first information layer of Example 3, itwas proved that the number of corroded points was reduced when the oxide(In₂O₃) of the element M was contained in the interface layers, and thenumber of corroded points did not sharply increase even after longhours, and further, the number of corroded points was able to be reducedmore reliably when In₂O₃ exceeding 10 mol % was contained. Furthermore,when the interface layers had a composition of ZrO₂-[(100−X)/2] mol %SiO₂—X mol % In₂O₃ (20≦X≦80 mol %), corrosion (separation) was notobserved even after 100 hours in the film corrosion test (at 90° C., 80%of relative humidity). When the interface layers had a composition ofZrO₂-[(100−X)/2] mol % SiO₂—X mol % In₂O₃ (30≦X≦70 mol %), corrosion(separation) was not observed even after 200 hours in the film corrosiontest (at 90° C., 80% of relative humidity).

As shown in Table 12, in the second information layer of Example 3, whenthe interface layers had a composition of ZrO₂-[(100−X)/2] mol % SiO₂—Xmol % In₂O₃ (20≦X≦80), corrosion (separation) was not observed after 100hours in the film corrosion test (at 90° C., 80% of relative humidity).When the interface layers had a composition of ZrO₂-[(100−X)/2] mol %SiO₂—X mol % In₂O₃ (40≦X≦60), corrosion (separation) was not observedafter 200 hours in the film corrosion test (at 90° C., 80% of relativehumidity).

As shown in Table 13, in the first information layer of Example 4, itwas proved that the number of corroded points was reduced when the oxide(In₂O₃) of the element M was contained in the interface layers, and thenumber of corroded points did not sharply increase even after longhours, and further, the number of corroded points was able to be reducedin a reliable manner when In₂O₃ exceeding 10 mol % was contained.Furthermore, when the interface layers had a composition of[46(ZrO₂)-4(Y₂O₃)]-[(100−X)/2] mol % SiO₂—X mol % In₂O₃ (20≦X≦80 mol %),corrosion (separation) was not observed even after 100 hours in the filmcorrosion test (at 90° C., 80% of relative humidity). When the interfacelayers had a composition of [46(ZrO₂)-4(Y₂O₃)]-[(100−X)/2] mol % SiO₂—Xmol % In₂O₃ (30≦X≦70 mol %), corrosion (separation) was not observedeven after 200 hours in the film corrosion test (at 90° C., 80% ofrelative humidity).

As shown in Table 14, in the second information layer of Example 4, whenthe interface layers had a composition of [46(ZrO₂)-4(Y₂O₃)]-[(100−X)/2]mol % SiO₂—X mol % In₂O₃ (20≦X≦80), corrosion (separation) was notobserved after 100 hours in the film corrosion test (at 90° C., 80% ofrelative humidity). When the interface layers had a composition of[46(ZrO₂)-4(Y₂O₃)]-[(100−X)/2] mol % SiO₂—X mol % In₂O₃ (40≦X≦60),corrosion (separation) was not observed after 200 hours in the filmcorrosion test (at 90° C., 80% of relative humidity).

It was proved from the results of Examples 2 to 4 as described abovethat the number of corroded points was able to be reduced when theinterface layers contained an oxide of element M contained in therecording layer, particularly, the increase in the number of thecorroded points after long hours was able to be suppressed effectively.Also, when the interface layers contained 10 mol % or more of the oxideof the element M, the number of the corroded points was able to bereduced more effectively. When the interface layers had a composition ofZrO₂—X mol % Ga₂O₃, ZrO₂-[(100−X)/2] mol % SiO₂—X mol % In₂O₃ or[46(ZrO₂)-4(Y₂O₃)]-[(100−X)/2] mol % SiO₂—X mol % In₂O₃, where X is in arange of 20≦X≦80 respectively, both the first information layers and thesecond information layers were allowed to obtain a high reliability. Thereliability further was increased with the first information layers whenX was in a range of 30≦X≦70. With the second information layers, thereliability further was increased when X was in a range of 40≦X≦60.Here, as a result, when X was in a range of 30≦X≦70, the secondinformation layers did not show further reliability improvement as muchas the first information layers did. However, considering the lifetimerequirement for commercial products, 30 years of lifetime at roomtemperature can still be guaranteed even with this range, so this resultshould be good enough. The differences of the film corrosion testresults between the first information layer and the second informationlayer may be due to the fact that each of the layers forming the secondinformation layer is thinner than the counterparts of the firstinformation layer, which probably reduces an effect of preventing waterfrom intruding into between the recording layer and the interface layerin the humidity resistance test. This result reveals that there is anoptimum value also for the amount of the oxide of the element M to bemixed in the interface layers, that is, 20≦X≦80 mol %, and furtherpreferably 30≦X≦70 mol %.

Examples 1, 2, 3, and 4 describe the cases where the element M in therecording layer and the oxide of the element M in the interface layerwere Ga and Ga oxide, and In and In oxide respectively. Similar resultsalso were obtained when the element M was Al or Mn as described in claim1.

Examples 1 and 2 describe the cases where the oxide of the element M wasmixed with Zr oxide as an oxide forming the interface layers. Example 3describes the case where Zr oxide and SiO₂ oxide were mixed as oxidesforming the interface layers. Example 4 further describes the case whereY oxide was mixed. However, the oxides to be used for the interfacelayers are not limited to these. Similar results also were obtained whenat least one oxide selected from Zr oxide, Si oxide, Cr oxide, Hf oxide,and Y oxide was mixed with the oxide of the element M.

Examples 1, 2, 3, and 4 describe the cases where the oxide of theelement M was mixed in all the interface layers 18, 20, 25, and 27 ofFIG. 1. And good results similarly were obtained in the film corrosiontest when the oxide of the element M was mixed only in either theinterface layer 18 or the interface layer 20, and when the oxide of theelement M was mixed only in either the interface layer 25 or theinterface layer 27. Also, when each of the interface layers 18, 20, 25,and 27 had a different composition, good results similarly were obtainedin the film corrosion test. For example, good results were obtained inthe cases where the interface layer 18, the recording layer 19 and theinterface layer 20 had a composition of (ZrO₂)₂₅(SiO₂)₂₅(In₂O₃)₅₀,Ge—Bi—Te—In, and (ZrO₂)₅₀(In₂O₃)₅₀ in this order respectively, and wherethe interface layer 25, the recording layer 26 and the interface layer27 had a composition of (ZrO₂)₄₀(SiO₂)₁₀(In₂O₃)₅₀, Ge—Bi—Te—In, and(ZrO₂)₆₀(SiO₂)₁₀(In₂O₃)₃₀ in this order respectively.

In the information recording medium of the present invention, when therecording layers had a composition range (a Ge—Bi—Te—M materialrepresented by Ge_(α)Bi_(β)Te_(γ)M_(100-α-βγ) (atom %)), good signalproperties were obtained in high speed recording prior to a life test,and good results similarly were obtained in the film corrosion tests inExamples 1, 2, 3, and 4.

Examples 1, 2, 3, and 4 describe the cases where the dielectric layers21 and 28 were composed of ZnS—SiO₂. Similar results also were obtainedwhen the dielectric layers 21 and 28 were composed of a materialcontaining at least one selected from Al₂O₃, SiO₂, Ta₂O₅, Mo—O, WO₃,ZrO₂, HfO₂, Al—N, B—N, Ge—N, Si—N, Ti—N, Zr—N, DyF₃, ErF₃, EuF₃, CeF₃,BiF₃, LaF₃, and ZnS, specifically, such as Ta₂O₅-50 mol % SiO₂, HfO₂-30mol % SiO₂-40 mol % Cr₂O₃, AlN-50 mol % SnO₂, ZrO₂-20 mol % SiO₂-30 mol% Cr₂O₃-20 mol % LaF₃, and CeF₃-80 mol % In₂O₃, which are not used inthe examples.

Examples 1, 2, 3, and 4 describe the cases where the reflective layer 16and the reflective layer 23 were formed of an Ag alloy. Similar resultsalso were obtained when the reflective layers 16 and the 23 contained,as their main component (at least 90 atom %), a material containing atleast one selected from Ag, Al, and Au, specifically, such as Al—Cr,Ag—Ga—Cu, and Ag—Pd—Cu, which are not used in the examples.

Examples 1, 2, 3, and 4 describe the cases where the high refractiveindex layer 22 was formed of an oxide of Ti. Similar results also wereobtained when the high refractive index layer 22 contained, as its maincomponent, a material containing at least one oxide selected from TiO₂and Nb₂O₅, specifically, such as TiO₂-10 mol % SiO₂ and TiO₂-50 mol %Nb₂O₅, which are not used in the examples. Similar results also wereobtained even when the high refractive index layer was not provideddepending on the disk configuration.

Examples 1, 2, 3, and 4 describe an information recording medium inwhich two information layers were stacked with an optical separationlayer interposed therebetween. Similar results also were obtained in thecase where only one information layer was provided (in the case whereonly the substrate 1, the first information layer 2, and the cover layer9 were provided, or in the case where only the substrate 1, the secondinformation layer 4, and the cover layer 9 were provided in FIG. 2).

INDUSTRIAL APPLICABILITY

An information recording medium of the present invention, a method andan apparatus for manufacturing the same can provide a highly reliableinformation recording medium that has excellent moisture resistance.Therefore, these are useful for high speed recording with a medium suchas Blu-ray Disc from the viewpoint of improving the reliability thereof.

1. An information recording medium, comprising: a recording layer whosephase can change by an optical or an electrical system so as to bedetectable, and an oxide layer that is in contact with the recordinglayer, wherein: the recording layer contains a Ge—Bi—Te-M materialrepresented by the following formula:Ge_(α)Bi_(β)Te_(γ)M_(100-α-β-γ)(atom %), where M denotes at least oneelement selected from Al, Ga, In and Mn, and α, β and γ satisfy 25≦α≦60,0<β≦18, 35≦γ≦55, and 82≦α+β+γ<100, and the oxide layer contains at leastone oxide of the element M contained in the recording layer.
 2. Theinformation recording medium according to claim 1, wherein the contentof the oxide of the element M in the oxide layer exceeds 10 mol %. 3.The information recording medium according to claim 2, wherein thecontent of the oxide of the element M in the oxide layer is 20 mol % orhigher and 80 mol % or lower.
 4. The information recording mediumaccording to claim 3, wherein the content of the oxide of the element Min the oxide layer is 30 mol % or higher and 70 mol % or lower.
 5. Theinformation recording medium according to claim 1, wherein the oxidelayer further contains at least one selected from Zr oxide, Si oxide, Croxide, Hf oxide, and Y oxide.
 6. The information recording mediumaccording to claim 1, comprising a plurality of information layers,wherein at least one of the plurality of information layers includes therecording layer and the oxide layer.
 7. The information recording mediumaccording to claim 1, wherein: at least a dielectric layer, therecording layer, and a reflective layer are provided in this order fromthe laser beam incident side, and the oxide layer is provided betweenthe dielectric layer and the recording layer or between the recordinglayer and the reflective layer, or both between the dielectric layer andthe recording layer and between the recording layer and the reflectivelayer.
 8. A method for manufacturing an information recording mediumincluding a recording layer whose phase can change by an optical or anelectrical system so as to be detectable, and an oxide layer that is incontact with the recording layer, the method comprising: (i) forming therecording layer containing a Ge—Bi—Te-M material represented by thefollowing formula:Ge_(α)Bi_(β)Te_(γ)M_(100-α-β-γ)(atom %), where α, β and γ satisfy25≦α≦60, 0 <β≦18, 35≦γ≦55, and 82≦α+β+γ<100, by a sputtering methodusing a first sputtering target containing Ge, Bi, Te, and element M,where M denotes at least one element selected from Al, Ga, In, and Mn,and (ii) forming the oxide layer containing at least one oxide of theelement M contained in the recording layer by a sputtering method usinga second sputtering target containing at least either one selected fromthe element M and an oxide of the element M.
 9. An apparatus formanufacturing an information recording medium to be used for themanufacturing method described in claim 8, the apparatus being providedwith a sputtering device that includes an electrode, the firstsputtering target or the second puttering target, and a substrate holderplaced facing the first sputtering target or the second sputteringtarget.